Method of pickling and coating stainless steel in the same bath



United States atent METHOD OF PICKLING AND COATING STAIN- LESS STEEL IN THE SAME BATH John A. Henricks', Logansport, Ind., assignor to Devex Corporation, Lakewood, Ohio, a corporation of Ohio No Drawing. Original application March 3, 1952, Serial No. 276,055. Divided and this application May 25, 1956, Serial No. 587,196

10 Claims. (Cl. 1486.14)

This is a continuation-in-part of application Serial No. 193,290, filed October 31, 1950, now issued as United States Letters Patent 2,588,234, and a division of copending application Serial No. 276,055, filed March 3, 1952, now abandoned. The invention relates to the lubrication of sliding metal surfaces and to the preparation of coating baths for such lubrication and to the meth d of forming lubricating surfaces on unpickled metal and to improvements in the pickling art.

In the formation of metal articles from hot metal scale usually forms on the metal which causes difiiculty in subsequent drawing operations. It has been the practice heretofore to eliminate such scale by suitable pickling baths and to provide a separate coating on the metal to insulate the metal from the die required for subsequent preforming operations.

It is an object of the present invention to improve the pickling art, to accelerate pickling operations, and to provide means whereby scale on the metal may be transformed into a fusible coating without appreciable loss or may be converted into lubricating film during pickling treatment.

Other objects will be apparent from the following description of the invention.

In accordance with one aspect of the invention, I accelerate the pickle by incorporating in the hydrochloric or sulfuric acid pickle baths, salts, containing oxygen and sulfur in which the valence ofsulfur is below six to remove the scale at a faster rate and to deposit concurrently a thin-film of iron sulfide on the metal surface. Suitable sulfur salts are the alkali and ammonium metal sulfites, bisulfites, hydrosulfites, thiosulfates, and tetrathionates. These salts accelerate the normal pickling action and also form a loose sulfide coating on the ferrous metal surface which is integrally fixed to the work by a hot water rinse preferably followed by a hot alkaline rinse. Preferably from one to ten pounds or around five pounds of the sulfur compound are added to the solution for each 100 gallons of pickle bath.

The above noted sulfur salts in acid solution give colloidal sulfur, sulfur dioxide, and various polythionic acids. The joint action of these materials is believed to be responsible for the acceleration of the pickling action and for the iron sulfide coating formed on the work.

The above noted salts up to maximum soluble amount are particularly valuable in descaling and sulfurizing stainless steel surfaces. The general practice is to descale stainless steels in a hot 15 to 30 percent hydrochloric acid bath or in a 12 to 25 percent sulfuric acid bath containing to 100 pounds of sodium chloride for each 100 gallons of solution. In this way I obtain a highly accelerated pickling bath that will remove scale in a small fraction of the time otherwise required.

The following examples illustrate this feature of my invention.

Example 1 In a previous operation heavily scaled stainless steel tubing was being successfully drawn with a 30 to 40 percent reduction by descaling the pierced annealed stainless billets for about 20 minutes in a fused caustic bath containing nitrate at temperature of 1000 F. The work was then quenched in water, rinsed, and then pickled about five minutes in 15% H 50 containing 15 lbs. NaCl per gallons of solution at a temperature of 195 F. The work was then rinsed and neutralized in 1% NaOH and again treated in the fused caustic for 15 minutes and again quenched, and again pickled in the salt sulfuric acid for 15 minutes, and then coated for drawing by immersion in a 15% sodium bifiuoride bath, activated by hydrochloric acid, colloidal sulfur, and sulfur dioxide for ten minutes at F. The total process time, not including rinsing, was about one hour and five minutes.

This same salt-sulfuric acid pickle was activated by the addition of 2 to 3 pounds of sodium thiosulfate per 100 gallons of pickle solution. Identical heavily scaled stock was then pickled for 10 minutes in the activated salt-sulfuric pickle, then rinsed and neutralized. The partially pickled stock was then immersed in the NaOI-INaNO fused bath for 5 minutes, then quenched and rinsed and again pickled 5 minutes in the activated salt-sulfuric acid. The stock was completely scale free after this cycle. The total process time, not including rinsing, was about 30 minutes. This example illustrates the time saving obtainable by activating the pickling bath in accordance with the subject invention.

This invention is equally useful in the processing of low carbon alloys. Rusted and scaled low carbon rod wire or discs are immersed in an accelerated pickling bath and are rapidly descaled and cleaned. Simultaneously, the stock is filmed with a layer of iron sulfide during the pickle. The stock is then rinsed in hot water or in hot water and a subsequent alkaline bath to fix the sulfide coating thereon. The stock is then drawn with or Without additional lubrication depending upon the circumstances. The iron sulfide film is an integral, meltable, non-scratchy coating which lubricates in the forming operations.

ExampleZ Low carbon steel blanks, circular in shape, were immersed in a 20% salt-sulfuric bath accelerated with five pounds of sodium acid sulfite per 100 gallons of salt sulfuric bath. The blanks were left in this solution for around eight minutes and then removed and rinsed in hot water. They were covered with a brownish-black sulfide layer. They were then filmed with soap and borax, dried, and drawn. The treated blanks were noticeably brighter and smoother than those pickled in unactivated salt-sulfuric pickle and drawn with soap and borax.

Example3 Low carbon rod is immersed in an 18% hydrochloric acid bath activated with three pounds of sodium thiosulfate for each 100 gallons of solution. The rods are left in solution long enough to be descaled and form a brownish-black sulfide film thereon. They are then rinsed in hot water and then in a tri-sodium phosphate solution and dried. This fixes the sulfide film on the rods. The rods are then drawn using soap and borax at the box. The drawn rod has a bright and scratch-free surface.

While in the aforementioned examples I have usually shown one fixed film over the integral coating of iron salt on the metal, I may use more than one film to obtain further benefits from stepwise lubrication. Thus, the surface of the steel to be worked may be treated with a solution such for example as the baths of Example 1 containing polythionate materials equivalent to Wackenroders solution to form an integral adhered coating of iron sulfide upon the material. The thus treated metal after rinsing may be then filmed by contacting it with an, alkaline earth polysulfide solution containing a colloidal carbohydrate such as starch or polyvinyl alcohol and the like. After drying the latter film on the metal it may be then quickly immersed in an aqueous soap and borax film such as previously described to provide a second film over the previous polysulfide film. The material thus treated may then be dried and subjected to extreme cold work.

Although several embodiments of the invention have been herein shown and described, it Will be understood that in accordance with the provisions of the patent statutes, numerous modifications of the construction shownmay be resorted to without departing from the spirit of the invention.

What I claim is:

1. The process of pickling and coating stainless steel in the same bath comprising the steps of immersing said work in a 12 to 30 percent acid pickling bath containing about 5 to 100 pounds of sodium-chloride and from 1 to pounds per 100 gallons of solution of an activator comprising an alkali salt containing oxygen and sulfur with a valence below six, and removing said work and rinsing in hot water,

2. The process of pickling and coating stainless steel surfaces in the same bath comprising the steps of subjecting them to contact with 10 to 30 percent acid pickling bath containing about 5 to 100 pounds of sodium chloride and 1 to 10 pounds per 100 gallons of pickling bath of an activator comprising salts containing oxygen and sulfur in which the valence of sulfur is below six, allowing said contact for a period of time long enough to form an iron sulfide film on the ferrous surface, and finally fixing said sulfide film on said ferrous surface by rinsing it in an alkaline rinse.

3. A method of pickling and coating stainless steel work surfaces in the same bath, comprising the step of; immersing said Work in 12 to 25 percent bath containing about 5 to 100 pounds of sodium chloride and from 1 to 10 pounds per 100 gallons of solution of an activator comprising an alkali salt containing oxygen and sulfur with a valence below six.

4. A 12 to 30 percent acid bath for simultaneously cleaning and coating stainless steel surfaces containing about 5 to 100 pounds sodium chloride and from 1 to 10 pounds per 100 gallons of bath solution of an activator iii consisting of an alkali salt containing oxygen and sulfur with a valence below six.

5. A 12 to 30 percent acid pickling bath for simultaneously cleaning and coating stainless steel surfaces containing about 5 to pounds sodium chloride and from 1 to 10 pounds per 100 gallons of bath solution of an activator comprising sodium thiosulfate.

6. A 12 to 25 percent sulfuric acid pickling bath for simultaneously cleaning and coating stainless steel surfaces containing about 5 to 100 pounds of sodium chloride and from 1 to 10 pounds of an activator consisting of an alkali salt containing oxygen and sulfur with a valence below six per 100 gallons of bath solution.

7. The bath of claim 6 in which theactivator is sodium thiosulfate.

8. A 15 to 30 percent hydrochloric acid pickling bath for simultaneously cleaning and coating stainless steel surfaces containing about 5 to 100 pounds sodium chloride and from 1 to 10 pounds of sodium thiosulfate per 100 gallons of bath solution.

9, A method of cleaning and coating stainless steel work surfaces comprising the steps of immersing said work in a fused caustic salt bath containing a descaling agent, removing the work from said salt bath and quenching and rinsing it to remove loose scale and alkaline residues, and then immersing said work in a 12 to 30 percent acid pickling bath for simultaneously cleaning and coating stainless steel surfaces containing about 5 to 100 pounds sodium chloride and 1 to 10 pounds per 100 gallons of solution of an activator comprising an alkali salt containing oxygen and sulfur with a valence below six.

10. The process of cleaning and coating work with ferrous surfaces comprising the steps of immersing said work in a 12 to 13 percent acid pickling bath for simultaneously cleaning and coating stainless steel surfaces containing in solution about 5 to 100 pounds sodium chloride and at least 1 pound per 100 gallons of solution of an activator comprising an alkali salt containing oxygen and sulfur with a valence below six, and removing said work and rinsing in hot water.

References Cited in the file of this patent UNITED STATES PATENTS 2,249,383 Hilty July 15, 1941 2,347,742 Keene May 2, 1944 2,550,660 Amundsen et al. May 1, 1951 2,636,009 Irwin Apr. 21, 1953 

1. THE PROCESS OF PICKLING AND COATING STAINLESS STEEL IN THE SAME BATH COMPRISING THE STEPS OF IMMERSING SAID WORK IN A 12 TO 30 PERCENT ACID PICKLING BATH CONTAINING ABOUT 5 TO 100 POUNDS OF SODIUM CHLORIDE AND FROM 1 TO 10 POUNDS PER 100 GALLONS OF SOLUTION OF AN ACTIVATOR COMPRISING AN ALKALI SALT CONTAINING OXYGEN AND SULFUR WITH A VALENCE BELOW SIX, AND REMOVING SAID WORK AND RINSING IN HOT WATER. 